The rather high casulties relating to accidents in tall buildings have encouraged inventions in the direction of safety systems for high rise buildings, and most of these inventions relate to life parachutes. However, because almost all disasters in tall buildings are caused by fire burning from the lower floors to the upper floors, the use of life parachutes in rescuing people trapped may not be effective due to strong wind or fire, rugged ground surface, or the user's improper use of the parachute or fear of jumping down.
There is also a kind of safety equipment which makes use of cable cars pulled by chains. These cars are ordinarily fixed to the balcony of each floor, and in case of fire, these cars can be descended to the groung manually or by means of motor. However, these cars are very bulky, and in practice, fixing them to the balconies is really a problem.
Prior art also teaches a portable life-saving device which comprises a housing, rollers wound with steel wire accommodated therewithin, a braking means consisting a pair of brakes, and a pair of handles provided on both sides of the housing. One end of the steel wire is secured to a firm object, and the wire is caused to pass through the braking means whereby the user may descend to the ground. The user may manipulate the brakes each disposed at the front end of the handles to grip the wire so as to slide along or halt. However, this prior art overlooks the fact that both the brakes and the wire are made of steel. When the brakes and the wire press against each other, as a result of their steel property, the wire will either become locked or slide along unimpeded, especially when the wire bears the weight of a heavy person, say, a man of 100 kg. In this case, the brakes may either lock the wire or allow the wire to slide along unobstructed. The result of the above-mentioned setback is that when the user is falling down from a high position, he or she may be unable to brake the falling motion and may crash to the ground, or the user may, in panic, grip the handles too hard that the wire is locked to stop further descent; but when the user releases the grip and turns the handles, he or she may fall swiftly down. In this case, the user may suffer from sudden halts and sudden fast descent. Therefore, even though this prior art provides a braking system, in practice, the user may not control the sliding speed at will. Such a drawback has rendered the above-mentioned invention of little use in rescuing people trapped in tall buildings.